The prior art is well documented with numerous examples of press feed mechanisms, such typically including a transfer station positioned in communication with a metal stamping or like machine. The transfer station serves the purpose of aligning and feeding a metal sheet (typically unrolled from a feed drum) into the stamping or other material pressing operation.
To this end, the extending edges of the metal sheet typically include cutout apertures or the like through which engage traversable gripping fingers for moving the sheet along the feed mechanism and into the press operation. The press feed mechanism further includes an arrangement of driving/driven rollers, typically including a displaceable upper roller (often via some type of cam arrangement) moved into and out of contact with a lower roller, between which is communicated the steel sheet.
Disadvantages associated with known press feed mechanisms include the limited degree of inter-adjustability which can be established between the rollers, e.g. such resulting in the upper adjustable roller displacing into either of fully engaged or fully released contact relative to the lower roller and interposed sheet. The result of this is to slow the rate of sheet feed (or advance) between iterative stamping operations, thereby negatively impacting productivity.
Existing press feed assemblies utilize some form of cam feed associated with a drive roller and include each of the oscillating cam feed apparatus of Gentile, U.S. Pat. No. 4,316,569, the high speed cam roll lifter for a press feeder of Johnson, U.S. Pat. No. 4,144,990 and the adjustable input shaft for a press feed of Gentile, U.S. Pat. No. 4,449,658. Additional references of note include Waddington, U.S. Pat. No. 5,150,022 (servo controlled pilot release for a press feeder) and Gentile, U.S. Pat. No. 5,755,370 (press feed with infinitely variable stock material engagement spacing).
Such feed assemblies as described accordingly constitute a final component of a roll uncoiling operation and which handle the transfer the uncoiled and straightened material roll from the initial straightening operation to the downstream located press or stamping operation. As also above described, the feed assembly further typically includes at least one drive roller in close proximity to one or more additional rollers for gripping and advancing the uncoiled material in a manner consisting with the input requirements of the downstream press operation.
Traditional pilot release of feed rollers, also described in the relevant commercial art as “roller venting” can be actuated by one or more air cylinders of various bore size, such as in order to release an upper located feed roll from a corresponding lower feed roll, such further occurring upon lifting the full travel of the cylinder to allow for maximum material thickness clearance according to the machine capacity. In certain instances, the requirement of the air cylinder imparting a full (excessive) travel or lift to the feed roller can be eliminated by the use of adjustable stroke cylinders, such as which can be accomplished in a manual type operation.
For these reasons, accurate controlling of the pilot function for lift rate/speed/travel is difficult to control and is typically results in the utilization of a pre-set motion/rate in the assembly, such further resulting in considerable inefficiencies of operation. It is also found that the return motion of the feed roll cannot be controlled via a given rate or speed and results in imparting undesirable effects onto the uncoiled feed material and as the feed roll contacts the material with uncontrolled force (such as further which take into account the full weight of the feed roll and the upper piloting assembly, or via a slide block assembly).
The net effect of these operational limitations is that they can cause undesirable marking of the uncoiled and fed material, this most notably found in sensitive surface finish materials. As such, combined factors including rate of return, pressure in the cylinder and resultant lift-off or travel cannot be controlled using current technologies and methods, this further evidenced by the position of the feed roll during the lift cycle with the air cylinder not being accurate and further limited by hard stops inside the cylinder or an adjustable threaded rod acting as a hard stop.